Engine device

ABSTRACT

When first switching of switching from a first purge of supplying evaporated fuel gas to an intake pipe through a first purge passage to a second purge of supplying the evaporated fuel gas to the intake pipe through a second purge passage occurs and then second switching of switching from the second purge to the first purge occurs, a purge concentration-related value is corrected to a value closer to a first stored value that is the purge concentration-related value immediately before the first switching than to a second stored value that is the purge concentration-related value immediately before the second switching.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2020-090133 filed on May 22, 2020, incorporated herein by reference inits entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to an engine device.

2. Description of Related Art

An engine device of the type in question has been hitherto proposed thatincludes a first purge passage through which evaporated fuel gascontaining evaporated fuel is supplied for purging to an intake pipe ofan engine, downstream of a throttle valve, and a second purge passagethrough which the evaporated fuel gas is supplied for purging to theintake pipe, upstream of a compressor of a turbocharger, by an ejectorthat generates a negative pressure using a supercharging pressure fromthe turbocharger (e.g., see Japanese Unexamined Patent ApplicationPublication No. 2019-052561). In this engine device, an intake pipepressure that is a pressure inside the intake pipe, downstream of thethrottle valve, and a pressure generated by the ejector are compared todetect through which of the first purge passage and the second purgepassage the purge is performed. When the purge passage switches betweenthe first purge passage and the second purge passage, controlcharacteristic data used for controlling a purge control valve isswitched between first control characteristic data suitable for thefirst purge passage and second control characteristic data suitable forthe second purge passage.

SUMMARY

In an engine device, the air-fuel ratio of the engine tends to beunstable during the second purge in which the purge passage is thesecond purge passage, compared with during the first purge in which thepurge passage is the first purge passage, due to factors including alonger time taken for the evaporated fuel gas to reach a combustionchamber of the engine and fluctuations of the supercharging pressure,both attributable to the longer path to the combustion chamber.Therefore, when a purge concentration-related value related to theconcentration of the evaporated fuel gas is learned (updated) based on adeviation of the air-fuel ratio from a required air-fuel ratio, theaccuracy of the purge concentration-related value (learned value) tendsto be low (a deviation of the learned value from a theoretical valuethat is theoretically expected tends to be large) during the secondpurge. This makes it necessary to correct the purgeconcentration-related value (learned value) to a more appropriate valueafter the second purge has switched to the first purge.

A main object of an engine device of the present disclosure is tocorrect the purge concentration-related value (learned value) to a moreappropriate value after the second purge has switched to the firstpurge.

The engine device of the present disclosure has adopted the followingsolutions to achieve this main object.

The gist of the engine device of the present disclosure is as follows:

An engine device including:

-   -   an engine that has a throttle valve disposed in an intake pipe        and a fuel injection valve and outputs power using fuel supplied        from a fuel tank;    -   a turbocharger having a compressor disposed in the intake pipe,        upstream of the throttle valve;    -   an evaporated fuel processing device having        -   a supply passage that splits into a first purge passage and            a second purge passage that are connected to the intake            pipe, downstream of the throttle valve, and supplies            evaporated fuel gas containing evaporated fuel generated            inside the fuel tank to the intake pipe,        -   an ejector having an intake port connected to a            recirculation passage extending from the intake pipe,            between the compressor and the throttle valve, an exhaust            port connected to the intake pipe, upstream of the            compressor, and a suction port connected to the second purge            passage, and        -   a purge control valve provided in the supply passage;    -   an air-fuel ratio sensor mounted on an exhaust pipe of the        engine; and    -   a controller that controls the fuel injection valve by setting a        required injection amount using a required load factor of the        engine and a purge correction amount that is based on a purge        concentration-related value related to the concentration of the        evaporated fuel gas, controls the purge control valve using a        driving duty based on a required purge ratio while a purge of        supplying the evaporated fuel gas to the intake pipe is        executed, and learns, during execution of the purge, the purge        concentration-related value based on an air-fuel ratio deviation        that is a deviation of an air-fuel ratio detected by the        air-fuel ratio sensor from a required air-fuel ratio, wherein

when first switching that is switching from a first purge of supplyingthe evaporated fuel gas to the intake pipe through the first purgepassage to a second purge of supplying the evaporated fuel gas to theintake pipe through the second purge passage occurs and then secondswitching that is switching from the second purge to the first purgeoccurs, the controller corrects the purge concentration-related value toa value closer to a first stored value that is the purgeconcentration-related value immediately before the first switching thanto a second stored value that is the purge concentration-related valueimmediately before the second switching.

In the engine device of the present disclosure, the fuel injection valveis controlled by setting the required injection amount using therequired load factor of the engine and the purge correction amount thatis based on the purge concentration-related value related to theconcentration of the evaporated fuel gas. The purge control valve iscontrolled using a driving duty based on the required purge ratio whilea purge of supplying the evaporated fuel gas to the intake pipe isexecuted. During execution of the purge, the purge concentration-relatedvalue is learned based on the air-fuel ratio deviation that is adeviation of the air-fuel ratio detected by the air-fuel ratio sensorfrom the required air-fuel ratio. When the first switching that isswitching from the first purge of supplying the evaporated fuel gas tothe intake pipe through the first purge passage to the second purge ofsupplying the evaporated fuel gas to the intake pipe through the secondpurge passage occurs and then the second switching that is switchingfrom the second purge to the first purge occurs, the controller correctsthe purge concentration-related value to a value closer to the firststored value that is the purge concentration-related value immediatelybefore the first switching than to the second stored value that is thepurge concentration-related value immediately before the secondswitching. The present inventors confirmed by experiment and analysisthat during the second purge, the purge concentration-related value(learned value) tended to undergo a great degree of change (as theabsolute value) compared with a theoretical degree of change that istheoretically expected. Therefore, correcting the purgeconcentration-related value (learned value) to a value closer to thefirst stored value than to the second stored value at the time ofoccurrence of the second switching can promptly correct the purgeconcentration-related value to a more appropriate value.

In the engine device of the present disclosure, the controller maycorrect the purge concentration-related value to a value closer to thefirst stored value when a difference between the second stored value andthe first stored value at the time of occurrence of the second switchingis large than when the difference is small. The present inventorsconfirmed by experiment and analysis that when the purgeconcentration-related value (learned value) underwent a greater degreeof change (as the absolute value) during the second purge, the purgeconcentration-related value tended to undergo a greater degree of changecompared with the theoretical degree of change. Therefore, correctingthe purge concentration-related value to a value closer to the firststored value when the difference between the second stored value and thefirst stored value at the time of occurrence of the second switching islarge than when the difference is small can promptly correct the purgeconcentration-related value to a value that is more sufficientlyappropriate.

In the engine device of the present disclosure, the controller maycorrect the purge concentration-related value within a range closer tothe second stored value when, at the time of occurrence of the secondswitching, a counter related to a time during which an intake airtemperature of the engine is equal to or higher than a predeterminedtemperature and the purge is not executed has a large value than whenthe counter has a small value. This is because when the time duringwhich the purge is not executed in a high-temperature environment islong, the influence that a deviation of the purge concentration-relatedvalue (learned value) from a theoretical value in learning of the purgeconcentration-related value during the second purge has on the secondstored value is expected to be small compared with the influence that adeviation of the purge concentration-related value (learned value) fromthe theoretical value due to evaporated fuel generated inside the fueltank (the influence of a purge not being executed) has on the secondstored value.

In this case, when a first condition that the intake air temperature isequal to or higher than the predetermined temperature and moreover thepurge is not being executed is met, the controller may increase thevalue of the counter. When a second condition that the intake airtemperature is lower than the predetermined temperature and moreover thepurge is being executed, or a third condition that the intake airtemperature is equal to or higher than the predetermined temperature andmoreover, of the purges, the second purge is being executed is met, thecontroller may retain the value of the counter. When none of the firstcondition, the second condition, and the third condition is met, thecontroller may decrease or reset the value of the counter. Thus, thecounter can be more appropriately set.

In the engine device of the present disclosure, when the secondswitching occurs, the controller may correct the purgeconcentration-related value as a sum of the first stored value and avalue that is obtained by subtracting the first stored value from thesecond stored value and then multiplying the resulting value by a factorthat is smaller than one.

In the engine device of the present disclosure, when, at the time ofoccurrence of the second switching, there is no permission history thathigh-duty control of making the driving duty higher than a predeterminedduty was permitted during the first purge before the second switching,the controller may prohibit the high-duty control and set the secondstored value as the purge concentration-related value. This is becausewhen the high-duty control is prohibited at the time of occurrence ofthe second switching, the purge concentration-related value is lesslikely to change significantly immediately thereafter.

In the engine device of the present disclosure, the controller may setthe required injection amount using the required load factor, anair-fuel ratio correction amount related to a deviation of the air-fuelratio sensor, and the purge correction amount, and when a predeterminedcondition is met, further set the air-fuel ratio correction amount foran applicable region to which a current intake air amount or load factorof the engine belongs among a plurality of regions into which a range ofthe intake air amount or the load factor is divided such that a regionof a larger intake air amount or a higher load factor has a larger widththan a region of a smaller intake air amount or a lower load factor.

In the engine device of the present disclosure, the controller maydetermine a dominant purge that is dominant one of the first purge andthe second purge, based on an ejector pressure that is a pressure at thesuction port of the ejector and on a value of a post-throttle-valvepressure that is a pressure inside the intake pipe, downstream of thethrottle valve, with an offset amount based on the cross-sectional areaof the second purge passage relative to the cross-sectional area of thefirst purge passage taken into account. Thus, the dominant purge can bemore appropriately determined compared with when the offset amount basedon the cross-sectional area of the second purge passage relative to thecross-sectional area of the first purge passage is not taken intoaccount. The “cross-sectional area” may be represented by a pipediameter.

In this case, the controller may set the offset amount such that theabsolute value of the offset amount as a negative value becomes largeras the absolute value of the post-throttle-valve pressure as a negativevalue becomes larger. This is because when the absolute value of thepost-throttle-valve pressure as a negative value is larger, theinfluence of the cross-sectional area of the second purge passagerelative to the cross-sectional area of the first purge passage isgreater.

Further, in this case, the controller may estimate the ejector pressurebased on a pressure difference between a supercharging pressure that isa pressure inside the intake pipe, between the compressor and thethrottle valve, and a pre-compressor pressure that is a pressure insidethe intake pipe, upstream of the compressor, and on the driving duty.Thus, the ejector pressure can be estimated.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like signs denote likeelements, and wherein:

FIG. 1 is a configuration diagram showing an overview of theconfiguration of an engine device 10;

FIG. 2 is a chart illustrating examples of input and output signals ofan electronic control unit 70;

FIG. 3 is a flowchart showing one example of a fuel injection controlroutine;

FIG. 4 is a chart illustrating one example of a plurality of load factorregions Rk [1] to Rk [n];

FIG. 5 is a flowchart showing one example of an air-fuel ratiocorrection amount setting routine;

FIG. 6 is a graph illustrating one example of an air-fuel ratiocorrection amount setting map;

FIG. 7 is a flowchart showing one example of a purge correction amountsetting routine;

FIG. 8 is a flowchart showing one example of a purge control routine;

FIG. 9 is a flowchart showing one example of a dominant purgedetermination routine;

FIG. 10 is a graph illustrating one example of an ejector pressuresetting map;

FIG. 11 is a graph illustrating one example of an offset amount settingmap when the cross-sectional area of a second purge passage 63 is smallrelatively to the cross-sectional area of a first purge passage 62;

FIG. 12 is a graph illustrating one example of a full-open purge flowrate estimation map;

FIG. 13 is a flowchart showing one example of a purgeconcentration-related value learning routine;

FIG. 14 is a graph illustrating one example of an update amount settingmap;

FIG. 15 is a flowchart showing one example of a reflection factorsetting routine;

FIG. 16 is a flowchart showing one example of a high-temperaturenon-execution counter setting routine; and

FIG. 17 is a view illustrating one example of the states of a dominantpurge flag Fpd and a purge concentration-related value Cp duringexecution of a purge.

DETAILED DESCRIPTION OF EMBODIMENTS

Next, a mode for carrying out the present disclosure will be describedusing an embodiment.

FIG. 1 is a configuration diagram showing an overview of theconfiguration of an engine device 10 as one embodiment of the presentdisclosure, and FIG. 2 is a chart illustrating examples of input andoutput signals of an electronic control unit 70. The engine device 10 ofthe embodiment is installed in ordinary vehicles that travel using powerfrom an engine 12, or various types of hybrid vehicles that are equippedwith a motor in addition to the engine 12. As shown in FIG. 1 and FIG.2, the engine device 10 includes the engine 12, a turbocharger 40, anevaporated fuel processing device 50, and the electronic control unit70.

The engine 12 is configured as an internal combustion engine thatoutputs power using fuel, such as gasoline or light oil, supplied from afuel tank 11. In the engine 12, air cleaned by an air cleaner 22 istaken into an intake pipe 23 and passed through an intercooler 25, athrottle valve 26, and a surge tank 27 in this order. Then, fuel isinjected from a cylinder injection valve 28 mounted on a combustionchamber 30 to the air taken into the combustion chamber 30 through anintake valve 29. The air and the fuel thus mixed together undergoexplosive combustion caused by an electric spark from a spark plug 31.The engine 12 converts reciprocating motion of a piston 32 that ispushed down by the energy of this explosive combustion into rotatingmotion of a crankshaft 14. Exhaust gas discharged from the combustionchamber 30 to an exhaust pipe 35 through an exhaust valve 34 isdischarged into outside air through exhaust gas control apparatuses 37,38 having a catalyst (three-way catalyst) that removes harmfulcomponents, such as carbon monoxide (CO), hydrocarbon (HC), and nitrogenoxides (NOx). The fuel is supplied from the fuel tank 11 to the cylinderinjection valve 28 through a feed pump 11 p, a low-pressure-side fuelpassage 17, a high-pressure pump 18, and a high-pressure-side fuelpassage 19. The high-pressure pump 18 is driven by power from the engine12 to pressurize the fuel in the low-pressure-side fuel passage 17 andsupply the pressurized fuel to the high-pressure-side fuel passage 19.

The turbocharger 40 is configured as a turbocharger including acompressor 41, a turbine 42, a rotating shaft 43, a wastegate valve 44,and a blow-off valve 45. The compressor 41 is disposed in the intakepipe 23, upstream of the intercooler 25. The turbine 42 is disposed inthe exhaust pipe 35, upstream of the exhaust gas control apparatus 37.The rotating shaft 43 couples the compressor 41 and the turbine 42 toeach other. The wastegate valve 44 is provided in a bypass pipe 36 thatcouples two points in the exhaust pipe 35, one upstream and the otherdownstream of the turbine 42, to each other, and is controlled by theelectronic control unit 70. The blow-off valve 45 is provided in abypass pipe 24 that couples two points in the intake pipe 23, oneupstream and the other downstream of the compressor 41, to each other,and is controlled by the electronic control unit 70.

In the turbocharger 40, the opening degree of the wastegate valve 44 isadjusted to thereby adjust the distribution ratio between the amount ofexhaust gas flowing through the bypass pipe 36 and the amount of exhaustgas flowing through the turbine 42, the rotary driving force of theturbine 42, the amount of air compressed by the compressor 41, and thesupercharging pressure (intake air pressure) of the engine 12.Specifically, the distribution ratio is adjusted such that when theopening degree of the wastegate valve 44 is smaller, the amount ofexhaust gas flowing through the bypass pipe 36 is smaller and the amountof exhaust gas flowing through the turbine 42 is larger. When thewastegate valve 44 is fully open, the engine 12 can operate like anaturally aspirated engine that is not equipped with the turbocharger40.

In the turbocharger 40, when the pressure inside the intake pipe 23,downstream of the compressor 41, is to some extent higher than thepressure upstream thereof, opening the blow-off valve 45 can release anexcessive pressure on a downstream side of the compressor 41. Instead ofbeing a valve controlled by the electronic control unit 70, the blow-offvalve 45 may be configured as a check valve that opens when the pressureinside the intake pipe 23, downstream of the compressor 41, becomes tosome extent higher than the pressure upstream thereof.

The evaporated fuel processing device 50 is a device that performs apurge of supplying evaporated fuel gas (purge gas) generated inside thefuel tank 11 to the intake pipe 23 of the engine 12, and includes anintroduction passage 52, an on-off valve 53, a bypass passage 54, reliefvalves 55 a, 55 b, a canister 56, a common passage 61, a first purgepassage 62, a second purge passage 63, a buffer part 64, a purge controlvalve 65, check valves 66, 67, a recirculation passage 68, and anejector 69. The introduction passage 52 and the common passage 61correspond to the “supply passage” of the embodiment.

The introduction passage 52 is connected to the fuel tank 11 and thecanister 56. The on-off valve 53 is provided in the introduction passage52 and configured as a normally closed solenoid valve. The on-off valve53 is controlled by the electronic control unit 70.

The bypass passage 54 forms a bypass connecting two points in theintroduction passage 52, one on the side of the fuel tank 11 and theother on the side of the canister 56 relative to the on-off valve 53,and has two branches 54 a, 54 b that split from the bypass passage 54and then merge. The relief valve 55 a is provided in the branch 54 a andconfigured as a check valve, and opens when the pressure on the side ofthe fuel tank 11 becomes to some extent higher than the pressure on theside of the canister 56. The relief valve 55 b is provided in the branch54 b and configured as a check valve, and opens when the pressure on theside of the canister 56 becomes to some extent higher than the pressureon the side of the fuel tank 11.

The canister 56 is connected to the introduction passage 52 and opens tothe atmosphere through an atmospheric release passage 57. An inside ofthe canister 56 is filled with an adsorbent, such as activated carbon,that can adsorb evaporated fuel from the fuel tank 11. The atmosphericrelease passage 57 is provided with an air filter 58.

The common passage 61 is connected to the introduction passage 52, nearthe canister 56, and splits at a split point 61 a into the first purgepassage 62 and the second purge passage 63. The first purge passage 62is connected to the intake pipe 23, between the throttle valve 26 andthe surge tank 27. The second purge passage 63 is connected to a suctionport of the ejector 69.

The buffer part 64 is provided in the common passage 61. An inside ofthe buffer part 64 is filled with an adsorbent, such as activatedcarbon, that can adsorb evaporated fuel from the fuel tank 11 and thecanister 56. The purge control valve 65 is provided in the commonpassage 61, on the side of the split point 61 a relative to the bufferpart 64. The purge control valve 65 is configured as a normally closedsolenoid valve. The purge control valve 65 is controlled by theelectronic control unit 70.

The check valve 66 is provided in the first purge passage 62, near thesplit point 61 a. The check valve 66 allows the evaporated fuel gas(purge gas) containing evaporated fuel to flow through a purge passage60 in a direction from the side of the common passage 61 toward the sideof the first purge passage 62 (intake pipe 23) and prohibits theevaporated fuel gas from flowing in the opposite direction. The checkvalve 67 is provided in the second purge passage 63, near the splitpoint 61 a. The check valve 67 allows the evaporated fuel gas to flowthrough the purge passage 60 in a direction from the side of the commonpassage 61 toward the side of the second purge passage 63 (ejector 69)and prohibits the evaporated fuel gas from flowing in the oppositedirection.

The recirculation passage 68 is connected to the intake pipe 23, betweenthe compressor 41 and the intercooler 25, and to an intake port of theejector 69. The ejector 69 has the intake port, the suction port, and anexhaust port. The ejector 69 has the intake port connected to therecirculation passage 68, the suction port connected to the second purgepassage 63, and the exhaust port connected to the intake pipe 23,upstream of the compressor 41. A leading end part of the intake port hasa tapered shape.

In the ejector 69, a pressure difference occurs between the intake portand the exhaust port when the turbocharger 40 is operating (when thepressure inside the intake pipe 23, between the compressor 41 and theintercooler 25, is a positive pressure), so that recirculating intakeair (intake air that is recirculated from downstream of the compressor41 in the intake pipe 23 through the recirculation passage 68) flowsfrom the intake port toward the exhaust port. As the recirculatingintake air is depressurized in the leading end part of the intake port,a negative pressure occurs near the leading end part. This negativepressure causes the evaporated fuel gas to be suctioned from the secondpurge passage 63 through the suction port, and this evaporated fuel gasis supplied, along with the recirculating intake air having a negativepressure, to the intake pipe 23, upstream of the compressor 41, throughthe exhaust port.

The evaporated fuel processing device 50 thus configured operatesbasically as follows: When the pressure inside the intake pipe 23,downstream of the throttle valve 26 (a surge pressure Ps to be describedlater) is a negative pressure and the on-off valve 53 and the purgecontrol valve 65 are open, the check valve 66 opens, so that evaporatedfuel gas (purge gas) generated inside the fuel tank 11 and evaporatedfuel gas desorbed from the canister 56 are supplied to the intake pipe23, downstream of the throttle valve 26, through the introductionpassage 52, the common passage 61, and the first purge passage 62.Hereinafter, this action will be referred to as a “downstream purge.” Inthis case, if the pressure inside the intake pipe 23, between thecompressor 41 and the intercooler 25 (a supercharging pressure Pc to bedescribed later) is a negative pressure or zero, the ejector 69 will notoperate and therefore the check valve 66 will not open.

When the pressure inside the intake pipe 23, between the compressor 41and the intercooler 25 (supercharging pressure Pc) is a positivepressure and the on-off valve 53 and the purge control valve 65 areopen, the ejector 69 operates and the check valve 67 opens, so that theevaporated fuel gas is supplied to the intake pipe 23, upstream of thecompressor 41, through the introduction passage 52, the common passage61, the second purge passage 63, and the ejector 69. Hereinafter, thisaction will be referred to as an “upstream purge.” In this case, thecheck valve 66 opens or closes according to the pressure inside theintake pipe 23, downstream of the throttle valve 26 (surge pressure Ps).

Thus, the evaporated fuel processing device 50 performs only thedownstream purge or the upstream purge of the two types of purges, orboth the downstream purge and the upstream purge, depending on thepressure inside the intake pipe 23, downstream of the throttle valve 26(surge pressure Ps) and the pressure inside the intake pipe 23, betweenthe compressor 41 and the intercooler 25 (supercharging pressure Pc).

The electronic control unit 70 is configured as a microprocessorcentered around a CPU, and incudes, in addition to the CPU, a ROM thatstores processing programs, a RAM that temporarily stores data, anon-volatile flash memory that stores and retains data, input and outputports, and a communication port. Signals from various sensors are inputinto the electronic control unit 70 through the input port.

Examples of the signals input into the electronic control unit 70include a tank internal pressure Ptnk from an internal pressure sensor11 a that detects the pressure inside the fuel tank 11; a crank angleθcr from a crank position sensor 14 a that detects the rotation positionof the crankshaft 14 of the engine 12; a coolant temperature Tw from acoolant temperature sensor 16 that detects the temperature of a coolantin the engine 12; and a throttle valve opening degree TH from a throttleposition sensor 26 a that detects the opening degree of the throttlevalve 26. A further example is a cam position θca from a cam positionsensor (not shown) that detects the rotation position of an intake camshaft that opens and closes the intake valve 29 or an exhaust cam shaftthat opens and closes the exhaust valve 34. Further examples are anintake air amount Qa from an air flow meter 23 a mounted on the intakepipe 23, upstream of the compressor 41; an intake air temperature Tinfrom an intake air temperature sensor 23 t mounted on the intake pipe23, upstream of the compressor 41; an intake air pressure(pre-compressor pressure) Pin from an intake air pressure sensor 23 bmounted on the intake pipe 23, upstream of the compressor 41; and thesupercharging pressure Pc from a supercharging pressure sensor 23 cmounted on the intake pipe 23, between the compressor 41 and theintercooler 25. Further examples are the surge pressure(post-throttle-valve pressure) Ps from a surge pressure sensor 27 amounted on the surge tank 27, and a surge temperature Ts from atemperature sensor 27 b mounted on the surge tank 27. A further exampleis a supply fuel pressure Pfd from a fuel pressure sensor 28 a thatdetects the fuel pressure of fuel supplied to the cylinder injectionvalve 28. Further examples are a front air-fuel ratio AF1 from a frontair-fuel ratio sensor 35 a mounted on the exhaust pipe 35, upstream ofthe exhaust gas control apparatus 37, and a rear air-fuel ratio AF2 froma rear air-fuel ratio sensor 35 b mounted on the exhaust pipe 35,between the exhaust gas control apparatus 37 and the exhaust gas controlapparatus 38. Further examples are an opening degree Opv of the purgecontrol valve 65 from a purge control valve position sensor 65 a, and asensor signal Pobd from an OBD sensor (pressure sensor) 63 a mounted inthe second purge passage 63.

Various control signals are output from the electronic control unit 70through the output port. Examples of the signals output from theelectronic control unit 70 include a control signal to the throttlevalve 26, a control signal to the cylinder injection valve 28, and acontrol signal to the spark plug 31. Further examples are a controlsignal to the wastegate valve 44, a control signal to the blow-off valve45, and a control signal to the on-off valve 53. Another example is acontrol signal to the purge control valve 65.

The electronic control unit 70 calculates a speed Ne and a load factor(a ratio of the volume of air actually taken into the engine 12 duringone cycle relative to the stroke volume per cycle of the engine 12) KLof the engine 12. The speed Ne is calculated based on the crank angleθcr from the crank position sensor 14 a. The load factor KL iscalculated based on the intake air amount Qa from the air flow meter 23a and the speed Ne.

In the engine device 10 of the embodiment thus configured, theelectronic control unit 70 performs, based on a required load factor KL*of the engine 12, modes of control including intake air amount controlof controlling the opening degree of the throttle valve 26, fuelinjection control of controlling the amount of fuel injected from thecylinder injection valve 28, ignition control of controlling theignition timing of the spark plug 31, supercharge control of controllingthe opening degree of the wastegate valve 44, and purge control ofcontrolling the opening degree of the purge control valve 65. In thefollowing, the fuel injection control and the purge control will bedescribed. The intake air amount control, the ignition control, and thesupercharge control do not constitute the core of the present disclosureand therefore a detailed description thereof will be omitted.

The fuel injection control will be described. FIG. 3 is a flowchartshowing one example of a fuel injection control routine. This routine isrepeatedly executed by the electronic control unit 70. When this routineis executed, the electronic control unit 70 inputs pieces of dataincluding the load factor KL of the engine 12, an air-fuel ratiocorrection amount α [i], and a purge correction amount β (step S100).

As the load factor KL of the engine 12, a value calculated based on theintake air amount Qa and the speed Ne is input. The air-fuel ratiocorrection amount α [i] is a correction amount related to a deviation(offset amount) of the front air-fuel ratio sensor 35 a for anapplicable region (a region number i (i: one of 1 to n)) to which acurrent load factor KL belongs among a plurality of load factor regionsRk [1] to Rk [n] (n: a total number of regions) into which the range ofthe load factor KL is divided. As the air-fuel ratio correction amount α[i], a value set by an air-fuel ratio correction amount setting routine,to be described later, is input. FIG. 4 is a chart illustrating oneexample of the load factor regions Rk [1] to Rk [n]. In the embodiment,as shown, the load factor regions Rk [1] to Rk [n] are set by dividing arange expected of the load factor KL into load factor regions Rk [1], .. . , Rk [n] in increasing order of the load factor KL such that theload factor region Rk [n] of the highest load factor has a larger width(covers a wider range of the load factor KL) than the other load factorregions Rk [1] to Rk [n−1]. The purge correction amount β is acorrection amount related to the downstream purge and the upstreampurge, and a value set by a purge correction amount setting routine, tobe described later, is input as the purge correction amount β.

Subsequently, a base injection amount Qfbs of the cylinder injectionvalve 28 is set based on the load factor KL (step S110), and a requiredinjection amount Qf* of the cylinder injection valve 28 is set by addingthe air-fuel ratio correction amount α [i] and the purge correctionamount β to the set base injection amount Qfbs (step S120). The cylinderinjection valve 28 is controlled using the set required injection amountQf* (step S130), and this routine is ended. The base injection amountQfbs is a base value of the required injection amount Qf* of thecylinder injection valve 28 that is required for the air-fuel ratio ofthe air-fuel mixture inside the combustion chamber 30 to meet a requiredair-fuel ratio AF*. As the base injection amount Qfbs, for example, avalue is set that is calculated as the product of the load factor KL anda unit injection amount (an amount of injection per 1% of the loadfactor KL) Qfpu of the cylinder injection valve 28 that is required forthe air-fuel ratio of the air-fuel mixture inside the combustion chamber30 to meet the required air-fuel ratio AF*.

Next, a process of setting air-fuel ratio correction amounts α [1] to α[n] for the respective load factor regions Rk [1] to Rk [n] used in thefuel injection amount control routine of FIG. 3 will be described usingthe air-fuel ratio correction amount setting routine of FIG. 5. Thisroutine is repeatedly executed by the electronic control unit 70. Untilset in the current trip, the air-fuel ratio correction amounts α [1] toα [n] for the respective load factor regions Rk [1] to Rk [n] haveinitial values or values that were set last during the last trip or anearlier trip.

When the air-fuel ratio correction amount setting routine of FIG. 5 isexecuted, the electronic control unit 70 first determines whether thisroutine is executed for the first time in the current trip (step S200).When it is determined that this routine is executed for the first timein the current trip, the electronic control unit 70 resets the values ofall setting completion flags Fα [1] to Fα [n] for the load factorregions Rk [1] to Rk [n] to zero as an initial value (step S210). Thesetting completion flags Fα [1] to Fα [n] are flags indicating whetherthe air-fuel ratio correction amounts α [1] to α [n] have been set inthe current trip. When it is determined in step S200 that this routineis executed not for the first time in the current trip, the process ofstep S210 is not executed.

Subsequently, the electronic control unit 70 inputs pieces of dataincluding the coolant temperature Tw and a steady operation flag Fst ofthe engine 12, and the region number i of the applicable region to whichthe current load factor KL belongs among the load factor regions Rk [1]to Rk [n] (step S220). As the coolant temperature Tw, a value detectedby the coolant temperature sensor 16 is input. As the steady operationflag Fst, a value set by a steady operation flag setting routine (notshown) is input. In the steady operation flag setting routine, theelectronic control unit 70 determines whether the engine 12 is in steadyoperation using at least one of the speed Ne, the intake air amount Qa,and the load factor KL of the engine 12. The electronic control unit 70sets the value of the steady operation flag Fst to one when it isdetermined that the engine 12 is in steady operation, and sets the valueof the steady operation flag Fst to zero when it is determined that theengine 12 is not in steady operation. As the region number i of theapplicable region, a value that is set based on the load factor KL andthe load factor regions Rk [1] to Rk [n] is input.

Then, the coolant temperature Tw is compared with a threshold valueTwref (step S230), and the value of the steady operation flag Fst ischecked (step S240). As the threshold value Twref, for example, about55° C. to 65° C. is used. The processes of steps S230 and S240 areprocesses of determining whether conditions for setting the air-fuelratio correction amount α [i] for the region number i are met. When thecoolant temperature Tw is lower than the threshold value Twref in stepS230, or when the value of the steady operation flag Fst is zero in stepS240, it is determined that the conditions for setting the air-fuelratio correction amount α [i] for the region number i are not met, andthis routine is ended.

When the coolant temperature Tw is equal to or higher than the thresholdvalue Twref in step S230 and the value of the steady operation flag Fstis one in step S240, it is determined that the conditions for settingthe air-fuel ratio correction amount α [i] for the region number i aremet, and the value of the setting completion flag Fα [i] for the regionnumber i is checked (step S250). When the value of the settingcompletion flag Fα [i] for the region number i is zero, it is determinedthat the air-fuel ratio correction amount α [i] for the region number ihas not been set in the current trip. Then, the front air-fuel ratio AF1is input (step S260), and the air-fuel ratio correction amount α [i] forthe region number i is set based on the input front air-fuel ratio AF1(step S270). The value of the setting completion flag Fα [i] for theregion number i is set to one (step S280), and this routine is ended.

As the front air-fuel ratio AF1, a value detected by the front air-fuelratio sensor 35 a is input. The air-fuel ratio correction amount α [i]for the region number i can be obtained by applying the front air-fuelratio AF1 at the time when the conditions for setting the air-fuel ratiocorrection amount α [i] are met to an air-fuel ratio correction amountsetting map. The air-fuel ratio correction amount setting map isspecified in advance by experiment or analysis as a relationship betweenthe front air-fuel ratio AF1 at the time when the conditions for settingthe air-fuel ratio correction amount α [i] for the region number i aremet and the air-fuel ratio correction amount α [i], and is stored in theROM or the flash memory (not shown). FIG. 6 is a graph illustrating oneexample of the air-fuel ratio correction amount setting map. As shown,the air-fuel ratio correction amount α [i] is set such that, when thefront air-fuel ratio AF1 at the time when the setting conditions are metis on a rich side or a lean side relative to the required air-fuel ratioAF*, the absolute value of the air-fuel ratio correction amount α [i]becomes larger within a negative range or a positive range as thedifference between the front air-fuel ratio AF1 and the requiredair-fuel ratio AF* becomes larger (as the front air-fuel ratio AF1deviates further from the required air-fuel ratio AF*). When theair-fuel ratio correction amount α [i] is smaller, the cylinderinjection valve 28 is controlled in the fuel injection control routineof FIG. 3 with the required injection amount Qf* reduced accordingly.Since the load factor regions Rk [1] to Rk [n] are set such that theload factor region Rk [n] of the highest load factor becomes wider thanthe other load factor regions Rk [1] to Rk [n−1] as described above (seeFIG. 4), the reliability of the air-fuel ratio correction amount α [n]for the load factor region Rk [n] is lower than the reliabilities of theair-fuel ratio correction amounts α [1] to α [n−1] for the load factorregions Rk [1] to Rk [n−1].

When the value of the setting completion flag Fα [i] for the regionnumber i is one in step S250, it is determined that the air-fuel ratiocorrection amount α [i] for the region number i has been set in thecurrent trip, and this routine is ended without the processes of stepsS260 to S280 being executed.

Next, a process of setting the purge correction amount β used in thefuel injection amount control routine of FIG. 3 will be described usingthe purge correction amount setting routine of FIG. 7. This routine isrepeatedly executed by the electronic control unit 70. When this routineis executed, the electronic control unit 70 first inputs pieces of dataincluding the intake air amount Qa, the opening degree Opv of the purgecontrol valve 65, the required purge ratio Rprq, and the purgeconcentration-related value Cp (step S300).

As the intake air amount Qa, a value detected by the air flow meter 23 ais input. As the opening degree Opv of the purge control valve 65, avalue detected by the purge control valve position sensor 65 a is input.As the required purge ratio Rprq, a value set by a purge controlroutine, to be described later, is input. The value of the requiredpurge ratio Rprq is set to zero when a purge condition, to be describedlater, is not met (when the purge control is not executed). The purgeconcentration-related value Cp is a correction factor related to thedeviation of the air-fuel ratio inside the combustion chamber 30 (thefront air-fuel ratio AF1 detected by the front air-fuel ratio sensor 35a) per 1% of the purge ratio from the required air-fuel ratio AF*. Whenthe purge concentration-related value Cp is a negative value, this meansthat a gas passing through the purge control valve 65 containsevaporated fuel, and when the purge concentration-related value Cp isequal to or larger than zero, this means that the gas passing throughthe purge control valve 65 does not contain evaporated fuel. As thepurge concentration-related value Cp, a value set by a purgeconcentration-related value learning routine, to be described later, isinput. The purge concentration-related value Cp is set to zero as aninitial value when a trip is started. The “purge concentration” meansthe concentration of evaporated fuel in evaporated fuel gas, and the“purge ratio” means the ratio of the evaporated fuel gas to an intakeair amount.

When the pieces of data are thus input, it is determined whether a purgeis being executed using the input opening degree Opv of the purgecontrol valve 65 (step S310). When it is determined that a purge is notbeing executed, the value of the purge correction amount β is set tozero (step S320), and this routine is ended.

When it is determined in step S310 that a purge is being executed, theproduct of the purge concentration-related value Cp, the intake airamount Qa, and the required purge ratio Rprq is set as the purgecorrection amount β (step S330), and this routine is ended. The purgecorrection amount β thus set has a negative value when the purgeconcentration-related value Cp is a negative value, and the absolutevalue of the purge correction amount β as a negative value becomeslarger as the absolute value of the purge concentration-related value Cpbecomes larger, and becomes larger as the intake air amount Qa or therequired purge ratio Rprq becomes larger or higher. The purge correctionamount β becomes zero when the purge concentration-related value Cp iszero. Further, the purge correction amount β has a positive value whenthe purge concentration-related value Cp is a positive value, and theabsolute value of the purge correction amount β as a positive valuebecomes larger as the absolute value of the purge concentration-relatedvalue Cp becomes larger, and becomes larger as the intake air amount Qaor the required purge ratio Rprq becomes larger or higher. When thepurge correction amount β is smaller, the cylinder injection valve 28 iscontrolled in the fuel injection control routine of FIG. 3 with therequired injection amount Qf* reduced accordingly.

Next, the purge control will be described. FIG. 8 is a flowchart showingone example of the purge control routine. FIG. 9 is a flowchart showingone example of a dominant purge determination routine for determining adominant purge that is dominant one of the downstream purge and theupstream purge. These routines are repeatedly executed by the electroniccontrol unit 70 when the purge condition is met (when a purge isexecuted). As the purge condition, for example, a condition is used thatoperation control (the fuel injection control etc.) of the engine 12 isbeing performed and the value of the setting completion flag Fα [i] forthe applicable region (region number i) to which the current load factorKL belongs among the load factor regions Rk [1] to Rk [n] is one (theair-fuel ratio correction amount α [i] has been set in the currenttrip). In the following, to simplify the description, determination ofthe dominant purge will be described first using the dominant purgedetermination routine of FIG. 9, and then the purge control based onthis determination will be described using the purge control routine ofFIG. 8.

When the dominant purge determination routine of FIG. 9 is executed, theelectronic control unit 70 first inputs pieces of data including theintake air pressure Pin, the supercharging pressure Pc, the surgepressure Ps, and a driving duty Ddr (step S500). As the intake airpressure Pin, a value detected by the intake air pressure sensor 23 b isinput. As the supercharging pressure Pc, a value detected by thesupercharging pressure sensor 23 c is input. As the surge pressure Ps, avalue detected by the surge pressure sensor 27 a is input. As thedriving duty Ddr, a value set by the purge control routine of FIG. 8 isinput.

When the pieces of data are thus input, an ejector pressure Pej isestimated based on a value obtained by subtracting the intake airpressure Pin from the supercharging pressure Pc and on the driving dutyDdr (step S510). The ejector pressure Pej can be obtained by applyingthe value obtained by subtracting the intake air pressure Pin from thesupercharging pressure Pc and the driving duty Ddr to an ejectorpressure setting map. The ejector pressure setting map is specified inadvance by experiment or analysis as a relationship among the valueobtained by subtracting the intake air pressure Pin from thesupercharging pressure Pc, the driving duty Ddr, and the ejectorpressure Pej, and is stored in the ROM or the flash memory (not shown).FIG. 10 is a graph illustrating one example of the ejector pressuresetting map. As shown, the ejector pressure Pej is set so as to becomehigher (have a smaller absolute value as a negative value) as thedriving duty Ddr becomes higher, and become lower (have a largerabsolute value as a negative value) as the supercharging pressure Pc(the value obtained by subtracting the intake air pressure Pin from thesupercharging pressure Pc) becomes higher.

Subsequently, based on the surge pressure Ps, an offset amount kd is setby which the surge pressure Ps is offset to correct the influence basedon the cross-sectional area of the second purge passage 63 relative tothe cross-sectional area of the first purge passage 62 (step S520). Theoffset amount kd can be obtained by applying the surge pressure Ps to anoffset amount setting map. The offset amount setting map is specified inadvance by experiment or analysis as a relationship between the surgepressure Ps and the offset amount kd, and is stored in the ROM or theflash memory (not shown). FIG. 11 is a graph illustrating one example ofthe offset amount setting map when the cross-sectional area of thesecond purge passage 63 is small relatively to the cross-sectional areaof the first purge passage 62. As shown, the offset amount kd is setsuch that the absolute value thereof as a negative value becomes largeras the absolute value of the surge pressure Ps as a negative valuebecomes larger. This is because the influence based on thecross-sectional area of the second purge passage 63 relative to thecross-sectional area of the first purge passage 62 becomes greater asthe absolute value of the surge pressure Ps as a negative value becomeslarger. When the first purge passage 62 and the second purge passage 63are formed by pipes, since the cross-sectional area is proportional tothe square of the pipe diameter, the influence based on thecross-sectional area of the second purge passage 63 relative to thecross-sectional area of the first purge passage 62 can be rephrased asan influence based on the pipe diameter of the second purge passagerelative to the pipe diameter of the first purge passage 62.

Then, the ejector pressure Pej and a value obtained by subtracting theoffset amount kd from the surge pressure Ps are compared (step S530).When it is determined that the ejector pressure Pej is equal to orhigher than the value obtained by subtracting the offset amount kd fromthe surge pressure Ps (the absolute value of the ejector pressure Pej asa negative value is equal to or smaller than that value), it isconcluded that the evaporated fuel gas flows dominantly through thefirst purge passage 62 (that the dominant purge is the downstreampurge). The value of a dominant purge flag Fpd is set to zero (stepS540), and this routine is ended.

When it is determined in step S530 that the ejector pressure Pej issmaller than the value obtained by subtracting the offset amount kd fromthe surge pressure Ps (the absolute value of the ejector pressure Pej asa negative value is larger than that value), it is concluded that theevaporated fuel gas flows dominantly through the second purge passage 63(that the dominant purge is the upstream purge). The value of thedominant purge flag Fpd is set to one (step S550), and this routine isended.

Thus, in the embodiment, the offset amount kd for correcting theinfluence based on the cross-sectional area of the second purge passagerelative to the cross-sectional area of the first purge passage 62 isset based on the surge pressure Ps, and the ejector pressure Pej and thevalue obtained by subtracting the offset amount kd from the surgepressure Ps are compared to determine which of the downstream purge andthe upstream purge is the dominant purge. In this way, the dominantpurge can be more appropriately determined than when the influence basedon the cross-sectional area of the second purge passage relative to thecross-sectional area of the first purge passage 62 is not taken intoaccount.

Next, the purge control will be described using the purge controlroutine of FIG. 8. When this routine is executed, the electronic controlunit 70 first inputs pieces of data including the intake air amount Qa,the intake air pressure Pin, the supercharging pressure Pc, the surgepressure Ps, the dominant purge flag Fpd, and a permission flag Fhi(step S400). As the intake air amount Qa, a value detected by the airflow meter 23 a is input. As the intake air pressure Pin, a valuedetected by the intake air pressure sensor 23 b is input. As thesupercharging pressure Pc, a value detected by the superchargingpressure sensor 23 c is input. As the surge pressure Ps, a valuedetected by the surge pressure sensor 27 a is input. As the dominantpurge flag Fpd, a value set by the dominant purge determination routineof FIG. 9 is input. The value of the permission flag Fhi is set to onewhen control of the purge control valve 65 using a high duty (a dutyhigher than a relatively low predetermined duty D1 to be describedlater) (hereinafter referred to as “high-duty control”) is permitted,and is set to zero when the high-duty control is prohibited. As thepermission flag Fhi, a value set by a purge concentration-related valuelearning routine, to be described later, is input. The value of thepermission flag Fhi is set to zero as an initial value when a trip isstarted.

Subsequently, a target purge ratio Rptg is set based on the dominantpurge flag Fpd (step S410). The target purge ratio Rptg is set so as toincrease gradually from a starting purge ratio Rpst1 (e.g., by rateprocessing using a rate value ΔRp1) during a period in which the purgecondition is met for the first time in each trip (a period from when thepurge condition starts to be met until meeting of the purge condition isinterrupted or ended). Further, the target purge ratio Rptg is set so asto increase gradually from a resuming purge ratio Rpst2 (e.g., by rateprocessing using a rate value ΔRp2) during a period in which the purgecondition is met for the second time or a subsequent time in each trip(a period from when meeting of the purge condition is resumed until itis interrupted or ended). As the starting purge ratio Rpst1 and theresuming purge ratio Rpst2, relatively small values are used to mitigatefluctuations in the air-fuel ratio of the engine 12. At least one of thevalue of the starting purge ratio Rpst1, the value of the resuming purgeratio Rpst2, and the rate values ΔRp1, ΔRp2 is set to a smaller valuewhen the value of the dominant purge flag Fpd is one, i.e., when thedominant purge is the upstream purge, than when the value of thedominant purge flag Fpd is zero, i.e., when the dominant purge is thedownstream purge. Examples of the case where meeting of the purgecondition is interrupted include a case where an accelerator pedal isreleased and fuel to the engine 12 is cut off while the vehicle equippedwith the engine device 10 is traveling.

Then, an upper-limit purge ratio Rplim is set based on the dominantpurge flag Fpd (step S420). The value of the upper-limit purge ratioRplim is set to a smaller value when the value of the dominant purgeflag Fpd is one, i.e., when the dominant purge is the upstream purge,than when the value of the dominant purge flag Fpd is zero, i.e., whenthe dominant purge is the downstream purge.

Further, a full-open purge flow rate Qpmax is estimated based on thesurge pressure Ps and the value obtained by subtracting the intake airpressure Pin from the supercharging pressure Pc (step S430). Thefull-open purge flow rate Qpmax is a purge flow rate (the volume flowrate of the evaporated fuel gas supplied to the intake pipe 23) when thedriving duty of the purge control valve 65 is 100%. The full-open purgeflow rate Qpmax can be obtained by applying the surge pressure Ps andthe value obtained by subtracting the intake air pressure Pin from thesupercharging pressure Pc to a full-open purge flow rate estimation map.The full-open purge flow rate estimation map is specified in advance byexperiment or analysis as a relationship among the surge pressure Ps,the value obtained by subtracting the intake air pressure Pin from thesupercharging pressure Pc, and the full-open purge flow rate Qpmax, andis stored in the ROM or the flash memory (not shown). FIG. 12 is a graphillustrating one example of the full-open purge flow rate estimationmap. As shown, the full-open purge flow rate Qpmax is set so as tobecome higher as the surge pressure Ps becomes lower (the absolute valuethereof as a negative value becomes larger) and as the value obtained bysubtracting the intake air pressure Pin from the supercharging pressurePc becomes larger.

In addition, a combustion chamber air amount Qcc that is an amount ofair inside the combustion chamber 30 is estimated based on the intakeair amount Qa and the pre-valve purge flow rate (past Qpv) of apredetermined time T1 ago (step S440). The pre-valve purge flow rate Qpvis a flow rate of the evaporated fuel gas in the common passage 61, onthe side of the introduction passage 52 relative to the purge controlvalve 65. If a purge was being executed the predetermined time T1 ago, avalue that is estimated by the process of step S490, to be describedlater, during execution of this routine of the predetermined time T1 agois used as the pre-valve flow rate (past Qpv) of the predetermined timeT1 ago, and if a purge was not being executed the predetermined time T1ago, zero is used as the value of the pre-valve flow rate of thepredetermined time T1 ago. The predetermined time T1 is specified as atime taken for the evaporated fuel gas in the common passage 61, on theside of the introduction passage 52 relative to the purge control valve65, to reach the combustion chamber 30. As the predetermined time T1, atime based on the dominant purge flag Fpd or the speed Ne of the engine12 may be used, or for simplicity's sake, a fixed time may be used. Thecombustion chamber air amount Qcc can be obtained by, for example,applying the intake air amount Qa and the past pre-valve purge flow rate(past Qpv) to a combustion chamber air amount estimation map. Thecombustion chamber air amount estimation map is specified in advance byexperiment or analysis as a relationship between the intake air amountQa and the past pre-valve purge flow rate (past Qpv), and the combustionchamber air amount Qcc, and is stored in the ROM or the flash memory(not shown).

When the full-open purge flow rate Qpmax and the combustion chamber airamount Qcc are thus estimated, a full-open purge ratio Rpmax isestimated based on these full-open purge flow rate Qpmax and combustionchamber air amount Qcc (step S450). The full-open purge ratio Rpmax canbe calculated by dividing the full-open purge flow rate Qpmax by thecombustion chamber air amount Qcc. Subsequently, the required purgeratio Rprq is set by limiting the target purge ratio Rptg by thefull-open purge ratio Rpmax and the upper-limit purge ratio Rplim (bysetting the upper limit) (step S460). Specifically, the smallest valueof the target purge ratio Rptg, the full-open purge ratio Rpmax, and theupper-limit purge ratio Rplim is set as the required purge ratio Rprq.

Then, the value of the permission flag Fhi is checked (step S470). Whenthe value of the permission flag Fhi is one, i.e., when the high-dutycontrol is permitted, the driving duty Ddr of the purge control valve 65is set by dividing the required purge ratio Rprq by the full-open purgeratio Rpmax (step S472), and the purge control valve 65 is controlledusing the set driving duty Ddr (step S480).

When the value of the permission flag Fhi is zero in step S470, i.e.,when the high-duty control is prohibited, the driving duty Ddr of thepurge control valve 65 is set by dividing the required purge ratio Rprqby the full-open purge ratio Rpmax and then limiting the resulting valueby the relatively low predetermined duty D1 (setting an upper limit)(step S474), and the purge control valve 65 is controlled using the setdriving duty Ddr (step S480).

Then, the pre-valve purge flow rate Qpv is estimated based on the intakeair amount Qa and the required purge ratio Rprq (step S490), and thisroutine is ended. The pre-valve purge flow rate Qpv can be obtained by,for example, applying the intake air amount Qa and the required purgeratio Rprq to a pre-valve purge flow rate estimation map. The pre-valvepurge flow rate estimation map is specified in advance by experiment oranalysis as a relationship between the intake air amount Qa and therequired purge ratio Rprq, and the pre-valve purge flow rate Qpv, and isstored in the ROM or the flash memory (not shown).

Thus, in the embodiment, the target purge ratio Rptg (at least one ofthe starting purge ratio Rpst1, the resuming purge ratio Rpst2, and therate values ΔRp1, ΔRp2) and the upper-limit purge ratio Rplim are variedaccording to which of the downstream purge and the upstream purge is thedominant purge. When the dominant purge is the upstream purge, comparedwith when the dominant purge is the downstream purge, the fuel injectioncontrol tends to make the front air-fuel ratio AF1 unstable due tofactors including a longer time taken for the evaporated fuel gas toreach the combustion chamber 30 of the engine 12 and fluctuations of thesupercharging pressure Pc, both attributable to the longer path to thecombustion chamber 30, as well as the lower reliability of the air-fuelratio correction amount α [n] for the load factor region Rk [n] than thereliabilities of the air-fuel ratio correction amounts α [1] to α [n−1]for the load factor regions Rk [1] to Rk [n−1]. In the embodiment, thetarget purge ratio Rptg and the upper-limit purge ratio Rplim are set tobe lower when the dominant purge is the upstream purge than when thedominant purge is the downstream purge, which can mitigate theinstability of the front air-fuel ratio AF1.

Next, a process of setting (learning) the purge concentration-relatedvalue Cp used for setting the purge correction amount β in the fuelinjection control routine of FIG. 3 will be described. FIG. 13 is aflowchart showing one example of a purge concentration-related valuelearning routine. This routine is repeatedly executed by the electroniccontrol unit 70. The value of the purge concentration-related value Cpis set to zero as an initial value when a trip is started.

When the purge concentration-related value learning routine of FIG. 13is executed, the electronic control unit 70 first inputs the openingdegree Opv of the purge control valve 65 (step S600), and determineswhether a purge is being executed using the input opening degree Opv ofthe purge control valve 65 (step S610). As the opening degree Opv of thepurge control valve 65, a value detected by the purge control valveposition sensor 65 a is input. When it is determined in step S610 that apurge is not being executed, a previous value of the purgeconcentration-related value Cp is retained (step S620), and this routineis ended.

When it is determined in step S610 that a purge is being executed, thefront air-fuel ratio AF1 and the dominant purge flag Fpd are input (stepS630). As the front air-fuel ratio AF1, a value detected by the frontair-fuel ratio sensor 35 a is input. As the dominant purge flag Fpd, avalue set by the dominant purge determination routine of FIG. 9 isinput.

When the pieces of data are thus input, previous and current values ofthe dominant purge flag (previous Fpd and current Fpd) are checked (stepS640). This process is a process of determining which of the followingfour cases applies: the previous and current dominant purges are thedownstream purge; the previous and current dominant purges are theupstream purge; first switching that is switching of the dominant purgefrom the downstream purge to the upstream purge has just occurred; andsecond switching that is switching of the dominant purge from theupstream purge to the downstream purge has just occurred. Since thedominant purge determination routine of FIG. 9 is repeatedly executedwhen the purge condition is met (when a purge is being executed) asdescribed above, these four cases include a case where a purge isinterrupted during a period from when the previous value of the dominantpurge flag (previous Fpd) is input to when the current value of thedominant purge flag (current Fpd) is input.

When both the previous and current values of the dominant purge flag(previous Fpd and current Fpd) are zero in step S640, i.e., when theprevious and current dominant purges are the downstream purge, theupdate amount γ is set based on the front air-fuel ratio AF1 (stepS650), and a value obtained by adding the update amount γ to theprevious purge concentration-related value (previous Cp) is set as a newpurge concentration-related value Cp (step S660). Thus, the purgeconcentration-related value Cp is learned (updated) while the dominantpurge is the downstream purge. Hereinafter, learning of the purgeconcentration-related value Cp while the dominant purge is thedownstream purge will be referred to as “downstream purge concentrationlearning.”

The update amount γ can be obtained by applying the front air-fuel ratioAF1 to an update amount setting map. The update amount setting map isspecified in advance by experiment or analysis as a relationship betweenthe front air-fuel ratio AF1 and the update amount γ, and is stored inthe ROM or the flash memory (not shown). FIG. 14 is a graph illustratingone example of the update amount setting map. As shown, the updateamount γ is set such that, when the front air-fuel ratio AF1 is on therich side or the lean side relative to the required air-fuel ratio AF*,the absolute value of the update amount γ becomes larger within anegative range or a positive range as the difference between the frontair-fuel ratio AF1 and the required air-fuel ratio AF* becomes larger(as the front air-fuel ratio AF1 deviates further from the requiredair-fuel ratio AF*). When the purge concentration-related value Cp thusset is a negative value, this means that the gas passing through thepurge control valve 65 contains evaporated fuel, and when the purgeconcentration-related value Cp is equal to or larger than zero, thismeans that the gas passing through the purge control valve 65 does notcontain evaporated fuel.

Subsequently, the value of a number of times of learning Ndn of thedownstream purge concentration learning is increased by one to update it(step S670). The value of the number of times of learning Ndn of thedownstream purge concentration learning is set to zero as an initialvalue when a trip is started. Then, it is determined whether the purgeconcentration-related value Cp is equal to or smaller than a negativethreshold value Cpref1 (step S680), and it is determined whether thenumber of times of learning Ndn of the downstream purge concentrationlearning is equal to or larger than a threshold value Ndnref (stepS690). The threshold value Cpref1 and the threshold value Ndnref arethreshold values used to determine whether completion conditions for thedownstream purge concentration learning are met. As the threshold valueCpref1, for example, about −10%/% to −15%/% is used. As the thresholdvalue Ndnref, for example, about 20 times to 40 times is used.

When it is determined in step S680 that the purge concentration-relatedvalue Cp is larger than the threshold value Cpref1 and it is determinedin step S690 that the number of times of learning Ndn of the downstreampurge concentration learning is smaller than the threshold value Ndnref,it is concluded that completion conditions for the downstream purgeconcentration learning are not met, and this routine is ended withoutthe permission flag Fhi and a permission history flag Fhidn beingchanged. The value of the permission flag Fhi is set to zero as aninitial value when a trip is started. The value of the permissionhistory flag Fhidn is set to zero as an initial value when a trip isstarted, and is set to one when the high-duty control is permitted whilethe dominant purge is the downstream purge (when the completionconditions for the downstream purge concentration learning are met).

When it is determined in step S680 that the purge concentration-relatedvalue Cp is equal to or smaller than the threshold value Cpref1 or it isdetermined in step S690 that the number of times of learning Ndn of thedownstream purge concentration learning is equal to or larger than thethreshold value Ndnref, it is concluded that the completion conditionsfor the downstream purge concentration learning are met. The value ofthe permission flag Fhi is set to one (step S700) and the value of thepermission history flag Fhidn is set to one (step S710), and thisroutine is ended. By this process, the high-duty control can bepermitted when the completion conditions for the downstream purgeconcentration learning are met. When the current value of the dominantpurge flag (current Fpd) is zero in step S640, the downstream purgeconcentration learning is performed by the process in step S650 andS660, regardless of whether the completion conditions for the downstreampurge concentration learning are met.

When both the previous and current values of the dominant purge flag(previous Fpd and current Fpd) are one in step S640, i.e., when theprevious and current dominant purges are the upstream purge, the updateamount γ is set and the purge concentration-related value Cp is set(steps S730 and S740), as in the process in steps S650 and S660. Thus,the purge concentration-related value Cp is learned (updated) also whenthe dominant purge is the upstream purge, as when the dominant purge isthe downstream purge. Hereinafter, learning of the purgeconcentration-related value Cp while the dominant purge is the upstreampurge will be referred to as “upstream purge concentration learning.”

Subsequently, a number of times of learning Nup of the upstream purgeconcentration learning is increased by one to update it (step S750). Thevalue of the number of times of learning Nup of the upstream purgeconcentration learning is set to zero as an initial value when a trip isstarted. Then, it is determined whether the purge concentration-relatedvalue Cp is equal to or smaller than a negative threshold value Cpref2(step S760), and it is determined whether the number of times oflearning Nup of the upstream purge concentration learning is equal to orlarger than a threshold value Nupref (step S770). The threshold valueCpref2 and the threshold value Nupref are threshold values used todetermine whether completion conditions for the upstream purgeconcentration learning are met. As the threshold value Cpref2, forexample, the same value as the threshold value Cpref1 is used. As thethreshold value Nupref, for example, the same value as the thresholdvalue Ndnref is used.

When it is determined in step S760 that the purge concentration-relatedvalue Cp is larger than the threshold value Cpref2 and it is determinedin step S770 that the number of times of learning Nup of the upstreampurge concentration learning is smaller than the threshold value Nupref,it is concluded that the completion conditions for the upstream purgeconcentration learning are not met, and this routine is ended withoutthe permission flag Fhi being changed (with the value zero or onethereof retained).

When it is determined in step S760 that the purge concentration-relatedvalue Cp is equal to or smaller than the threshold value Cpref2 or it isdetermined in step S770 that the number of times of learning Nup of theupstream purge concentration learning is equal to or larger than thethreshold value Nupref, it is concluded that the completion conditionsfor the upstream purge concentration learning are met. The value of thepermission flag Fhi is set to one (step S780), and this routine isended. By this process, the high-duty control can be permitted when thecompletion conditions for the upstream purge concentration learning aremet, even when the high-duty control was not permitted while thedominant purge was the downstream purge. Thus, the inconvenience of notbeing able to permit the high-duty control and increase the purge ratiowhile the dominant purge is the upstream purge is less likely to arise.When the current value of the dominant purge flag (current Fpd) is onein step S640, the upstream purge concentration learning is performed bythe process in step S760 and S770, regardless of whether the completionconditions for the upstream purge concentration learning are met.

When the previous value of the dominant purge flag (previous Fpd) iszero and the current value of the dominant purge flag (current Fpd) isone in step S640, i.e., when the first switching that is switching ofthe dominant purge from the downstream purge to the upstream purge hasjust occurred, the previous purge concentration-related value (previousCp), i.e., the purge concentration-related value Cp immediately beforethe first switching, is set as a first stored value Cpset1 (step S720),and the process in step S730 and the subsequent steps are executed.

When the previous value of the dominant purge flag (previous Fpd) is oneand the current value of the dominant purge flag (current Fpd) is zeroin step S640, i.e., when the second switching that is switching of thedominant purge from the upstream purge to the downstream purge has justoccurred, the previous purge concentration-related value (previous Cp),i.e., the purge concentration-related value Cp immediately before thesecond switching, is set as a second stored value Cpset2 (step S790).

Subsequently, the value of the permission history flag Fhidn is checked(step S800). This process is a process of determining, when the firstswitching that is switching of the dominant purge from the previousdownstream purge to the upstream purge occurs and then the secondswitching that is switching from the upstream purge to the currentdownstream purge occurs, whether there is a history that the high-dutycontrol was permitted (the completion conditions for the downstreampurge concentration learning were met) while the dominant purge was thedownstream purge before the second switching.

When the value of the permission history flag Fhidn is one in step S800,it is concluded that there is a history that the high-duty control waspermitted while the dominant purge was the downstream purge before thesecond switching, and the value of the permission flag Fhi is retained.When the values of the permission flag Fhi and the permission historyflag Fhidn were set to one while the dominant purge was the previous orearlier downstream purge, the value one of the permission flag Fhi andthe permission history flag Fhidn is retained when the dominant purgebecomes the upstream purge thereafter. Therefore, when the dominantpurge becomes the current downstream purge, the value one of thepermission flag Fhi is retained, i.e., permission of the high-dutycontrol is retained.

When the value of the permission history flag Fhidn is zero in stepS800, it is concluded that there is no history that the high-dutycontrol was permitted while the dominant purge was the downstream purgebefore the second switching, and the value of the permission flag Fhi isset to zero (step S810). Cases where the value of the permission historyflag Fhidn is zero in step S800 include a case where the value of thepermission flag Fhi was switched to one and a case where the value wasnot switched to one, between the first switching and the secondswitching (while the dominant purge was the upstream purge). Therefore,when the value of the permission history flag Fhidn is zero in stepS800, the value of the permission flag Fhi is switched from one to zero,or the value zero thereof is retained, i.e., permission of the high-dutycontrol is switched to prohibition thereof, or prohibition thereof isretained.

As described above, the fuel injection control tends to make the frontair-fuel ratio AF1 unstable when the dominant purge is the upstreampurge compared with when the dominant purge is the downstream purge.Thus, the accuracy of the purge concentration-related value Cp (learnedvalue) tends to be lower (a deviation of the learned value from atheoretical value that is theoretically expected tends to be larger)when the dominant purge is the upstream purge than when the dominantpurge is the downstream purge. Therefore, when there is no history thatthe high-duty control was permitted (the completion conditions for thedownstream purge concentration learning were met) while the dominantpurge was the previous or earlier downstream purge, and moreover thehigh-duty control was permitted while the dominant purge was theupstream purge, if the high-duty control is continuously permitted afterthe dominant purge switches to the current downstream purge, theair-fuel ratio of the engine 12 may fluctuate for reasons such as thatthe downstream purge concentration learning was not performed under thehigh-duty control. In the embodiment, however, when there is no historythat the high-duty control was permitted while the dominant purge wasthe previous or earlier downstream purge and moreover the high-dutycontrol was permitted while the dominant purge was the upstream purge,permission of the high-duty control is switched to prohibition thereofat the time of switching of the dominant purge to the current downstreampurge. This can mitigate fluctuations in the air-fuel ratio of theengine 12 after the dominant purge has switched from the upstream purgeto the downstream purge.

Subsequently, a value obtained by subtracting the first stored valueCpset1 (the purge concentration-related value Cp immediately before thefirst switching) from the second stored value Cpset2 (the purgeconcentration-related value Cp immediately before the second switching)is set as an amount of change ΔCp during the upstream purge that is anamount of change in the purge concentration-related value Cp while thedominant purge is the upstream purge (step S820). Then, a reflectionfactor kr that is equal to or smaller than one is set by a reflectionfactor setting routine to be described later (step S830). As shown inFormula (1), a sum of the first stored value Cpset1 and a value obtainedby multiplying the amount of change ΔCp during the upstream purge by thereflection factor kr is set as the purge concentration-related value Cp(step S840). Thus, when the value of the reflection factor kr is smallerthan one, the purge concentration-related value Cp is set to a valuecloser to the first stored value Cpset1 than to the second stored valueCpset2. More specifically, the purge concentration-related value Cp isset to a value closer to the first stored value Cpset1 when thereflection factor kr is smaller. When the value of the reflection factorkr is one, the second stored value Cpset2 is set as the purgeconcentration-related value Cp.

Cp=Cpset1+ΔCp·kr  (1)

Then, the update amount γ is set as in the process in step S650described above (step S850). The purge concentration-related value Cp isre-set by adding the update amount γ to the purge concentration-relatedvalue (previous Cp) set in step S840 (step S860), and the process instep S670 and the subsequent steps are executed.

Next, the process in step S830 of the purge concentration-related valuelearning routine of FIG. 13, i.e., the process of setting the reflectionfactor kr, will be described using the reflection factor setting routineof FIG. 15. When this routine is executed, the electronic control unit70 first checks the value of the permission history flag Fhidn (stepS900). Like the process in step S800 of the purge concentration-relatedvalue learning routine of FIG. 13, this process is a process of, whenthe first switching occurs and then the second switching occurs,determining whether there is a history that the high-duty control waspermitted (the completion conditions for the downstream purgeconcentration learning were met) while the dominant purge was thedownstream purge before the second switching.

When the value of the permission history flag Fhidn is one in step S900,it is concluded that there is a history that the high-duty control waspermitted while the dominant purge was the downstream purge before thesecond switching, and a high-temperature non-execution counter Cnp isinput (step S910). The high-temperature non-execution counter Cnp is acounter related to a time during which a purge is not executed in ahigh-temperature environment. As the high-temperature non-executioncounter Cnp, a value set by the high-temperature non-execution countersetting routine of FIG. 16 is input. The value of the high-temperaturenon-execution counter Cnp is set to zero as an initial value when a tripis started. Here, the description of the reflection factor settingroutine of FIG. 15 will be suspended to describe the high-temperaturenon-execution counter setting routine of FIG. 16.

The high-temperature non-execution counter setting routine of FIG. 16 isrepeatedly executed by the electronic control unit 70. When this routineis executed, the electronic control unit 70 first inputs pieces of dataincluding the intake air temperature Tin of the engine 12 and theopening degree Opv of the purge control valve 65 (step S1000). As theintake air temperature Tin, a value detected by the intake airtemperature sensor 23 t is input. As the opening degree Opv of the purgecontrol valve 65, a value detected by the purge control valve positionsensor 65 a is input.

Subsequently, it is determined whether the intake air temperature Tin ofthe engine 12 is equal to or higher than a threshold value Tinref (stepS1010), and it is determined whether a purge is being executed using theopening degree Opv of the purge control valve 65 (step S1020 or stepS1030). The threshold value Tinref is a threshold value used todetermine whether the intake air temperature Tin of the engine 12 ishigh. As the threshold value Tinref, for example, about 50° C. to 65° C.is used.

When it is determined in step S1010 that the intake air temperature Tinis equal to or higher than the threshold value Tinref and it isdetermined in step S1020 that a purge is not being executed, the valueof the high-temperature non-execution counter Cnp is increased by one toupdate it (step S1040), and this routine is ended.

When it is determined in step S1010 that the intake air temperature Tinis lower than the threshold value Tinref and it is determined in stepS1030 that a purge is being executed, the previous value of thehigh-temperature non-execution counter Cnp is retained (step S1070), andthis routine is ended.

When it is determined in step S1010 that the intake air temperature Tinis lower than the threshold value Tinref and it is determined in stepS1030 that a purge is not being executed, the value of thehigh-temperature non-execution counter Cnp is decreased by one to updateit as a value limited by zero (by setting a lower limit) (step S1100),and this routine is ended.

When it is determined in step S1010 that the intake air temperature Tinis equal to or higher than the threshold value Tinref and it isdetermined in step S1020 that a purge is being executed, the dominantpurge flag Fpd is input (step S1050). As the dominant purge flag Fpd, avalue set by the dominant purge determination routine of FIG. 9 isinput. Subsequently, the value of the dominant purge flag Fpd is checked(step S1060). When the value of the dominant purge flag Fpd is one,i.e., when the dominant purge is the upstream purge, the previous valueof the high-temperature non-execution counter Cnp is retained (stepS1070), and this routine is ended.

When the value of the dominant purge flag Fpd is zero in step S1060,i.e., when the dominant purge is the downstream purge, a post-resumptionnumber of times of learning Ncp3 that is a number of times the purgeconcentration-related value Cp is learned after resumption of a purgewhen a purge is interrupted and then resumed is input (step S1080), andthe post-resumption number of times of learning Ncp3 is compared with athreshold value Ncpref3 (step S1090). The threshold value Ncpref3 is athreshold value used to determine whether learning of the purgeconcentration-related value Cp has progressed since resumption of apurge. As the threshold value Ncpref3, for example, about three times toten times is used.

When the post-resumption number of times of learning Ncp3 is smallerthan the threshold value Ncpref3 in step S1090, the value of thehigh-temperature non-execution counter Cnp is decreased by one to updateit as a value limited by zero (by setting a lower limit) (step S1100),and this routine is ended. When the post-resumption number of times oflearning Ncp3 is equal to or larger than the threshold value Ncpref3 instep S1090, the value of the high-temperature non-execution counter Cnpis reset to zero (step S1110), and this routine is ended.

The high-temperature non-execution counter setting routine of FIG. 16has been described. The description of the reflection factor settingroutine of FIG. 15 will be resumed. When the high-temperaturenon-execution counter Cnp is input in step S910, the inputhigh-temperature non-execution counter Cnp is compared with a thresholdvalue Cnpref (step S920). The threshold value Cnpref is a thresholdvalue used to determine whether a time during which a purge is notexecuted in a high-temperature environment is long. As the thresholdvalue Cnpref, for example, 10 s to 20 s is used.

When the high-temperature non-execution counter Cnp is smaller than thethreshold value Cnpref in step S920, it is concluded that the timeduring which a purge is not executed in a high-temperature environmentis not long, and the absolute value of the amount of change ΔCp duringthe upstream purge is compared with a threshold value ΔCpref (stepS930). The threshold value ΔCpref is a threshold value used to determinewhether the purge concentration-related value Cp changed significantlybetween the first switching and the second switching (while the dominantpurge was the upstream purge). As the threshold value ΔCpref, forexample, about 3%/% to 7%/% is used.

When the absolute value of the amount of change ΔCp during the upstreampurge is smaller than the threshold value ΔCpref in step S930, it isconcluded that the purge concentration-related value Cp did notsignificantly change between the first switching and the secondswitching. The value of the reflection factor kr is set to kr1 that issmaller than one (step S940), and this routine is ended. When theabsolute value of the amount of change ΔCp during the upstream purge isequal to or larger than the threshold value ΔCpref in step S930, it isconcluded that the purge concentration-related value Cp changedsignificantly between the first switching and the second switching, andthe value of the reflection factor kr is set to kr2 that is smaller thankr1 (step S950), and this routine is ended. When the reflection factorkr is thus set, by the process in step S840 of the purgeconcentration-related value learning routine of FIG. 13, the purgeconcentration-related value Cp is set to a value closer to the firststored value Cpset1 than to the second stored value Cpset2. Morespecifically, the purge concentration-related value Cp is set to a valuecloser to the first stored value Cpset1 as the reflection factor kr issmaller.

The accuracy of the purge concentration-related value Cp (learned value)tends to be lower (the deviation of the learned value from thetheoretical value tends to be larger) when the dominant purge is theupstream purge than when the dominant purge is the downstream purge. Thepresent inventors confirmed by experiment and analysis that when thedominant purge was the upstream purge, the purge concentration-relatedvalue Cp tended to undergo a great degree of change (as the absolutevalue) compared with a theoretical degree of change that wastheoretically expected, and that the purge concentration-related valueCp tended to undergo a greater degree of change relatively to thetheoretical degree of change when the absolute value of the amount ofchange ΔCp during the upstream purge was larger. In the embodiment,therefore, the reflection factor kr is set to a smaller value and thepurge concentration-related value Cp is set to a value closer to thefirst stored value Cpset1 when, at the time of occurrence of the secondswitching, the absolute value of the amount of change ΔCp during theupstream purge is equal to or larger than the threshold value ΔCprefthan when the absolute value of the amount of change ΔCp during theupstream purge is smaller than the threshold value ΔCpref. Thus, whenthe second switching occurs, the purge concentration-related value Cpcan be promptly corrected to a more appropriate value. As a result,fluctuations in the air-fuel ratio of the engine 12 after the secondswitching occurs can be mitigated. The reflection factor kr is specifiedbased on a degree to which the degree of change in the purgeconcentration-related value Cp becomes greater relatively to thetheoretical degree of change. For example, when it is found byexperiment and analysis that in the case where the absolute value of theamount of change ΔCp during the upstream purge is smaller than thethreshold value ΔCpref and in the case where the absolute value is equalto or larger than the threshold value ΔCpref, the purgeconcentration-related value Cp undergoes degrees of change that areabout 10% and about 20%, respectively, greater than the theoreticaldegree of change, it is preferable that about 0.9 and about 0.8 be usedas the reflection factor kr for the former case and the latter case,respectively.

When the value of the high-temperature non-execution counter Cnp isequal to or larger than the threshold value Cnpref in step S920, it isconcluded that the time during which a purge is not executed in ahigh-temperature environment is long, and the value of the reflectionfactor kr is set to kr3 that is smaller than one and larger than kr1 andkr2 described above (step S960), and this routine is ended.

When the time during which a purge is not executed in a high-temperatureenvironment is long, the influence that the decrease in the accuracy ofthe purge concentration-related value Cp (learned value) in the upstreampurge concentration learning (the deviation of the learned value fromthe theoretical value) has on the second stored value Cpset2 is expectedto be small compared with the influence that the deviation of the purgeconcentration-related value Cp (learned value) from the theoreticalvalue due to evaporated fuel generated inside the fuel tank 11 (theinfluence of a purge not being executed) has on the second stored valueCpset2. In the embodiment, therefore, the reflection factor kr is set toa larger value and the purge concentration-related value Cp is set to avalue closer to the second stored value Cpset2 when the value of thehigh-temperature non-execution counter Cnp is equal to or larger thanthe threshold value Cnpref at the time of occurrence of the secondswitching than when the value of the high-temperature non-executioncounter Cnp is smaller than the threshold value Cnpref. Thus, when thesecond switching occurs, the purge concentration-related value Cp can bepromptly corrected to a more appropriate value.

When the value of the permission history flag Fhidn is zero in stepS900, it is concluded that there is no history that the high-dutycontrol was permitted while the dominant purge was the downstream purgebefore the second switching. The value of the reflection factor kr isset to one (step S970), and this routine is ended.

In the embodiment, as described above, when, at the time of occurrenceof the second switching, there is no history that the high-duty controlwas permitted while the dominant purge was the downstream purge beforethe second switching, permission of the high-duty control is switched toprohibition thereof, or prohibition thereof is retained. Thus, in thiscase, the purge concentration-related value Cp is less likely to changesignificantly immediately after the second switching. In the embodiment,therefore, when, at the time of occurrence of the second switching,there is no history that the high-duty control was permitted while thedominant purge was the downstream purge before the second switching, thepurge concentration-related value Cpset is set as the purgeconcentration-related value Cp. Thus, the purge-concentration-relatedvalue Cp can be set to an appropriate value.

FIG. 17 is a view illustrating one example of the states of the dominantpurge flag Fpd and the purge concentration-related value Cp duringexecution of a purge. FIG. 17 shows the states when the value of thepermission history flag Fhidn is one (when the value of the reflectionfactor kr is set to a value smaller than one) at the time of occurrenceof the second switching. As shown, when the first switching occurs (timet11) and then the second switching occurs (time t12), the purgeconcentration-related value Cp is corrected using the reflection factorkr and the amount of change ΔCp during the upstream purge that isobtained by subtracting the first stored value Cpset1 from the secondstored value Cpset2. Thus, the purge concentration-related value Cp canbe corrected to a more appropriate value.

In the engine device 10 of the embodiment having been described above,when the first switching that is switching of the dominant purge fromthe downstream purge to the upstream purge occurs and then the secondswitching that is switching of the dominant purge from the upstreampurge to the downstream purge occurs, the purge concentration-relatedvalue Cp is set to a value closer to the first stored value Cpset1 thatis the purge concentration-related value Cp immediately before the firstswitching than to the second stored value Cpset2 that is the purgeconcentration-related value Cp immediately before the second switching.Thus, when the second switching occurs, the purge concentration-relatedvalue Cp can be promptly corrected to a more appropriate value.

In the engine device 10 of the embodiment, in the case where the valueof the permission history flag Fhidn is one and the value of thehigh-temperature non-execution counter Cnp is smaller than the thresholdvalue Cnpref at the time of occurrence of the second switching, when theabsolute value of the amount of change ΔCp during the upstream purge issmaller than the threshold value ΔCpref, the value of the reflectionfactor kr is set to kr1, and when the absolute value of the amount ofchange ΔCp during the upstream purge is equal to or larger than thethreshold value ΔCpref, the value of the reflection factor kr is set tokr2 that is smaller than kr1. However, in the case where the value ofthe permission history flag Fhidn is one and the value of thehigh-temperature non-execution counter Cnp is smaller than the thresholdvalue Cnpref at the time of occurrence of the second switching, thereflection factor kr may be set so as to become smaller continuously, orstepwise in multiple stages, as the absolute value of the amount ofchange ΔCp during the upstream purge becomes larger.

In the engine device 10 of the embodiment, when the second switchingoccurs, the reflection factor kr is set based on the permission historyflag Fhidn, which of the value of the high-temperature non-executioncounter Cnp and the threshold value Cnpref is larger, and which of theabsolute value of the amount of change ΔCp during the upstream purge andthe threshold value ΔCpref is larger, and the purgeconcentration-related value Cp is corrected based on the first storedvalue Cpset1, the amount of change ΔCp during the upstream purge, andthe reflection factor kr. However, the reflection factor kr may be setwithin a range smaller than one, without taking the permission historyflag Fhidn into account. The reflection factor kr may be set withouttaking into account which of the value of the high-temperaturenon-execution counter Cnp and the threshold value Cnpref is larger.Further, the reflection factor kr may be set without taking into accountwhich of the absolute value of the amount of change ΔCp during theupstream purge and the threshold value ΔCpref is larger.

In the engine device 10 of the embodiment, the value of thehigh-temperature non-execution counter Cnp is increased when the firstcondition that the intake air temperature Tin is equal to or higher thanthe threshold value Tinref and moreover a purge is not being executed ismet. The value of the high-temperature non-execution counter Cnp isretained when the second condition that the intake air temperature Tinis lower than the threshold value Tinref and moreover a purge is beingexecuted, or the third condition that the intake air temperature Tin isequal to or higher than the threshold value Tinref and moreover theupstream purge is being executed (the value of the dominant purge flagFpd is one) is met. In the case where none of the first condition, thesecond condition, and the third condition is met, when thepost-resumption number of times of learning Ncp3 is smaller than thethreshold value Ncpref3, the value of the high-temperature non-executioncounter Cnp is decreased, and when the post-resumption number of timesof learning Ncp3 is equal to or larger than the threshold value Ncpref3,the value of the high-temperature non-execution counter Cnp is reset tozero. However, the applicable embodiment is not limited to this example.For example, when the first condition is met, the value of thehigh-temperature non-execution counter Cnp may be increased, and whenthe first condition is not met, the value of the high-temperaturenon-execution counter Cnp may be decreased or reset to zero.

In the engine device 10 of the embodiment, the target purge ratio Rptg(at least one of the starting purge ratio Rpst1, the resuming purgeratio Rpst2, and the rate values ΔRp1, ΔRp2) and the upper-limit purgeratio Rplim are varied according to which of the downstream purge andthe upstream purge is the dominant purge. However, only either thetarget purge ratio Rptg or the upper-limit purge ratio Rplim may bevaried according to which of the downstream purge and the upstream purgeis the dominant purge, or other parameters related to control of thepurge control valve 65 than the target purge ratio Rptg and theupper-limit purge ratio Rplim may be varied.

In the engine device 10 of the embodiment, the offset amount kd is setbased on the surge pressure Ps, and which of the downstream purge andthe upstream purge is the dominant purge is determined based on theejector pressure Pej and the value obtained by subtracting the offsetamount kd from the surge pressure Ps. However, which of the downstreampurge and the upstream purge is the dominant purge may be determinedbased on the ejector pressure Pej and a value obtained by subtracting afixed offset amount kd, irrelevant of the surge pressure Ps, from thesurge pressure Ps. Also in this case, which of the downstream purge andthe upstream purge is the dominant purge can be appropriatelydetermined, albeit with less accuracy than in the embodiment, comparedwith when the influence based on the cross-sectional area of the secondpurge passage relative to the cross-sectional area of the first purgepassage 62 is not taken into account.

In the engine device 10 of the embodiment, the air-fuel ratio correctionamounts α [1] to α [n] are set only once in each trip for the respectiveload factor regions Rk [1] to Rk [n]. However, the air-fuel ratiocorrection amounts α [1] to α [n] may be set multiple times during onetrip. In this case, the process of step S250 in the air-fuel ratiocorrection amount setting routine of FIG. 5 need not be executed.

In the engine device 10 of the embodiment, the range expected of theload factor KL is divided into the load factor regions Rk [1] to Rk [n],and the air-fuel ratio correction amounts α [1] to α [n] for therespective load factor regions Rk [1] to Rk [n] are set. Instead ofthis, a range expected of the intake air amount Qa may be divided into aplurality of air amount regions Rq [1] to Rq [n], and air-fuel ratiocorrection amounts α [1] to α [n] for the respective air amount regionsRq [1] to Rq [n] may be set.

In the engine device 10 of the embodiment, which of the downstream purgeand the upstream purge is the dominant purge is determined based on theejector pressure Pej and the value obtained by subtracting the offsetamount kd from the surge pressure Ps. However, which of the downstreampurge and the upstream purge is the dominant purge may be determinedbased on the load factor KL and the intake air amount Qa. In this case,which of the downstream purge and the upstream purge is the dominantpurge may be determined based on the load factor KL and a value at aborder between the load factor region Rk [n−1] and the load factorregion Rk [n], or which of the downstream purge and the upstream purgeis the dominant purge may be determined based on the intake air amountQa and a value at a border between the air amount region Rq [n−1] andthe air amount region Rq [n].

In the engine device 10 of the embodiment, the engine 12 includes thecylinder injection valve 28 that injects fuel into the combustionchamber 30. However, in addition to or in place of the cylinderinjection valve 28, the engine 12 may include a port injection valvethat injects fuel into the suction port.

In the engine device 10 of the embodiment, the turbocharger 40 isconfigured as a turbocharger in which the compressor 41 disposed in theintake pipe 23 and the turbine 42 disposed in the exhaust pipe 35 arecoupled to each other through the rotating shaft 43. Instead of this,the turbocharger 40 may be configured as a supercharger in which acompressor driven by the engine 12 or a motor is disposed in the intakepipe 23.

In the engine device 10 of the embodiment, the common passage 61 of theevaporated fuel processing device 50 is connected to the introductionpassage 52, near the canister 56. However, the common passage 61 may beconnected to the canister 56.

In the embodiment, the present disclosure is implemented in the form ofthe engine device 10 that is installed in ordinary cars or varioushybrid cars. However, the present disclosure may be implemented in theform of an engine device that is installed in a vehicle other than acar, or in the form of an engine device that is installed in stationaryequipment, such as construction equipment.

Since the embodiment is an example for specifically describing the modefor carrying out the disclosure described in the section SUMMARY,correspondence relationships between the major elements of theembodiment and the major elements of the disclosure described in thatsection do not limit the elements of the disclosure described in thatsection. Thus, the disclosure described in the section SUMMARY should beinterpreted based on the description in that section, and the embodimentis merely a specific example of the disclosure described in thatsection.

While the mode for carrying out the present disclosure has beendescribed above using the embodiment, it should be understood that thepresent disclosure is in no way limited to such an embodiment but can beimplemented in various forms within the scope of the gist of thedisclosure.

The present disclosure is applicable to the engine device manufacturingindustry and the like.

What is claimed is:
 1. An engine device comprising: an engine that has athrottle valve disposed in an intake pipe and a fuel injection valve andoutputs power using fuel supplied from a fuel tank; a turbochargerhaving a compressor disposed in the intake pipe, upstream of thethrottle valve; an evaporated fuel processing device having a supplypassage that splits into a first purge passage and a second purgepassage that are connected to the intake pipe, downstream of thethrottle valve, and supplies evaporated fuel gas containing evaporatedfuel generated inside the fuel tank to the intake pipe, an ejectorhaving an intake port connected to a recirculation passage extendingfrom the intake pipe, between the compressor and the throttle valve, anexhaust port connected to the intake pipe, upstream of the compressor,and a suction port connected to the second purge passage, and a purgecontrol valve provided in the supply passage; an air-fuel ratio sensormounted on an exhaust pipe of the engine; and a controller that controlsthe fuel injection valve by setting a required injection amount using arequired load factor of the engine and a purge correction amount that isbased on a purge concentration-related value related to a concentrationof the evaporated fuel gas, controls the purge control valve using adriving duty based on a required purge ratio while a purge of supplyingthe evaporated fuel gas to the intake pipe is executed, and learns,during execution of the purge, the purge concentration-related valuebased on an air-fuel ratio deviation that is a deviation of an air-fuelratio detected by the air-fuel ratio sensor from a required air-fuelratio, wherein when first switching that is switching from a first purgeof supplying the evaporated fuel gas to the intake pipe through thefirst purge passage to a second purge of supplying the evaporated fuelgas to the intake pipe through the second purge passage occurs and thensecond switching that is switching from the second purge to the firstpurge occurs, the controller corrects the purge concentration-relatedvalue to a value closer to a first stored value that is the purgeconcentration-related value immediately before the first switching thanto a second stored value that is the purge concentration-related valueimmediately before the second switching.
 2. The engine device accordingto claim 1, wherein the controller corrects the purgeconcentration-related value to a value closer to the first stored valuewhen a difference between the second stored value and the first storedvalue at a time of occurrence of the second switching is large than whenthe difference is small.
 3. The engine device according to claim 1,wherein the controller corrects the purge concentration-related valuewithin a range closer to the second stored value when, at a time ofoccurrence of the second switching, a counter related to a time duringwhich an intake air temperature of the engine is equal to or higher thana predetermined temperature and the purge is not executed has a largevalue than when the counter has a small value.
 4. The engine deviceaccording to claim 3, wherein: when a first condition that the intakeair temperature is equal to or higher than the predetermined temperatureand moreover the purge is not being executed is met, the controllerincreases the value of the counter; when a second condition that theintake air temperature is lower than the predetermined temperature andmoreover the purge is being executed, or a third condition that theintake air temperature is equal to or higher than the predeterminedtemperature and moreover, of the purges, the second purge is beingexecuted is met, the controller retains the value of the counter; andwhen none of the first condition, the second condition, and the thirdcondition is met, the controller decreases or resets the value of thecounter.
 5. The engine device according to claim 1, wherein, when thesecond switching occurs, the controller corrects the purgeconcentration-related value as a sum of the first stored value and avalue that is obtained by subtracting the first stored value from thesecond stored value and then multiplying the resulting value by a factorthat is smaller than one.
 6. The engine device according to claim 1,wherein, when, at a time of occurrence of the second switching, there isno permission history that high-duty control of making the driving dutyhigher than a predetermined duty was permitted during the first purgebefore the second switching, the controller prohibits the high-dutycontrol and sets the second stored value as the purgeconcentration-related value.
 7. The engine device according to claim 1,wherein the controller sets the required injection amount using therequired load factor, an air-fuel ratio correction amount related to adeviation of the air-fuel ratio sensor, and the purge correction amount,and when a predetermined condition is met, further sets the air-fuelratio correction amount for an applicable region to which a currentintake air amount or load factor of the engine belongs among a pluralityof regions into which a range of the intake air amount or the loadfactor is divided such that a region of a larger intake air amount or ahigher load factor has a larger width than a region of a smaller intakeair amount or a lower load factor.
 8. The engine device according toclaim 1, wherein the controller determines a dominant purge that isdominant one of the first purge and the second purge, based on anejector pressure that is a pressure at the suction port of the ejectorand on a value of a post-throttle-valve pressure that is a pressureinside the intake pipe, downstream of the throttle valve, with an offsetamount based on a cross-sectional area of the second purge passagerelative to a cross-sectional area of the first purge passage taken intoaccount.